1. Technical Field
The present invention relates to a liquid ejecting head such as an ink jet recording head and a method of manufacturing the same. In particular, the invention relates to a liquid ejecting head having crystalline material in which a nozzle is formed by an etching process, and to a method of manufacturing the same.
2. Related Art
For example, a liquid ejecting apparatus has a liquid ejecting head that ejects liquid through nozzles. The liquid ejecting apparatus ejects various liquids from the liquid ejecting head. An example of such liquid ejecting apparatuses is an image recording apparatus such as an ink jet printer (hereinafter referred to simply as a printer). The ink jet printer has an ink jet recording head (hereinafter referred to simply as a recording head) which is a liquid ejecting head. Ink in liquid form is ejected through nozzles of the recording head and lands on a recording medium (the object of ejection) such as a recording sheet. An image or the like is thus recorded. Moreover, recently liquid ejecting apparatuses have been applied not only to the image recording apparatus, but also to various manufacturing apparatuses such as an apparatus for manufacturing color filters of liquid crystal displays.
One such recording head has a nozzle substrate in which a plurality of rows of nozzles through which ink is ejected are provided, and pressure chambers that communicate with the nozzles. The pressures in the pressure chambers are changed by a pressure-generating unit, and ink is ejected through the nozzles by using the pressure changes. The pressure-generating unit may be a piezoelectric-type unit that uses a piezoelectric element, a thermal-type unit that uses a heat-generating element, an electrostatic-type unit that uses electrostatic force, or the like.
To fabricate the nozzle substrate, a plate member made of a metal such as stainless steel is plastically deformed with a punch and thereby nozzles are provided therein, for example (see JP-A-05-229127, for example). Each of the nozzles has a cylindrical straight portion on the ejection side, and a tapered portion that is continuous with the straight portion and that increases in diameter from the straight-portion side toward the pressure-chamber side. In order to ensure that a predetermined amount of ink lands at a predetermined location, the nozzles need to be dimensioned and shaped very precisely. Moreover, in order to record a more precise high-resolution image, it has been proposed to fabricate a nozzle plate from a single-crystal silicon substrate (hereinafter referred to simply as a silicon substrate) and form nozzles in the substrate by an etching process (for example, see JP-A-2007-175992). Nozzles formed by an etching process can have a higher degree of dimensional accuracy than nozzles formed by plastic deformation.
When a nozzle is formed in a silicon substrate by an etching process, it is difficult to form the above-mentioned tapered portion. For this reason, a plurality of cylindrical nozzle sections having different diameters and communicating with one another are formed so as to constitute a nozzle having a plurality of sections. Thus, an ink-ejecting characteristic similar to that of the above-described tapered nozzle is obtained. The nozzle section that is located at the ejection-side end has the smallest diameter, and the nozzle sections have successively larger diameters toward the pressure-chamber side. Here, flow-path resistance and inertance of the entire nozzle are considered, and successively different diameters are given to the nozzle sections in this manner so that the desired ink-ejecting characteristic can be obtained.
FIG. 8 is a sectional view of the main part of a nozzle having a plurality of cylindrical nozzle sections as described above, and illustrates the ejection of ink (displacement of the meniscus). In FIG. 8, the upper side is the pressure-chamber side, and the lower side is the ejection side. In a steady-state condition, the meniscus is located near the ejection-side opening of the nozzle. To eject ink, first, the pressure chamber is expanded and the pressure in the pressure chamber is decreased. As a result, the meniscus is drawn toward the pressure-chamber side (FIGS. 8A and 8B). When the meniscus has moved to near the boundary between a first nozzle section on the ejection side and a second nozzle section on the pressure-chamber side, the pressure chamber which has been expanded is rapidly contracted, and the pressure in the pressure chamber is increased. As a result, the middle of the meniscus swells and is pushed toward the ejection side (FIG. 8C). Thereafter, to separate an ink droplet from the meniscus, the pressure chamber is again expanded (FIG. 8D). There is a step portion (a surface that joins adjacent nozzle sections) between the nozzle section on the ejection side and the nozzle section on the pressure-chamber side. In particular, this kind of nozzle tends to have a relatively large difference in diameter between nozzle sections, and have a large step portion. When the pressure chamber is expanded for the second time after the rapid contraction, an entraining flow of ink tends to occur near the step portion from the inner-circumferential-surface side of the nozzle toward the middle of the meniscus, as indicated by arrows in FIG. 8D. More specifically, while the flow of ink at portions relatively remote from the step portion is parallel to the inner wall of the nozzle, a flow of ink parallel to the surface of the step portion occurs near the step portion. Thus, the flow of ink becomes complex and vortices tend to occur. Consequently, there is a risk that bubbles B will be entrained in the ink, as illustrated in FIG. 8E. If such bubbles B are created, there is a risk that the flight of ink will be distorted, and so on. Thus, there is a risk that the ejection of ink will be unstable.